Paper by Vincent Consonni 2020

Here you will find the paper by Vincent Consonni
" Owing to the chemical instability of ZnO nanowires and to their large surface area exhibiting a high density of traps, the use of a protective, passivating shell plays a major role in the performances of many devices. We show that a conformal TiO₂ shell can be grown on the ZnO nanowires by a double-step process using atomic layer deposition and postdeposition thermal treatment in air. An in situ analysis of the crystallization process of the amorphous TiO_x shell grown by atomic layer deposition is achieved in detail by temperature-dependent Raman scattering and X-ray diffraction measurements, indicating that the crystallization starts around 280 °C in air and that only the anatase phase is formed. It is further revealed from transmission electron microscopy-based experiments that the TiO₂ shell with the anatase phase is epitaxially grown on the ZnO nanowires with a range of orientation relationships. Interestingly, the epitaxial TiO₂ shell has a beneficial passivating effect and its crystallization resulting from the postdeposition thermal treatment at 350 °C in air leads to the redistribution of the hydrogen-related defects in the center of the ZnO nanowires, as shown by steady-state and time-resolved photoluminescence measurements. These findings demonstrate that the atomic layer deposition technique coupled with a postdeposition thermal treatment is a powerful tool to form ZnO/TiO₂ core–shell nanowire heterostructures with high structural and optical quality. They open the way for developing the present double-step process in other nanostructured material systems to master their related surface and interface properties."